Are cold thyroid nodules cancerous?

Only occassionally: While almost all thyroid cancers are cold, so are most benign nodules. If the nodule is hot, it is extremely rare for it to be cancer. If it is cold and looks suspicious on an ultrasound performed or at least interpreted by a very experienced clinician, it should be biopsied to see if surgery is necessary.

Not necessarily: Cold thyroid nodules can be cancerous but are usually benign. The next step is usually a biopsy, which is much mor helpful than a thyroid scan to distinguish thyroid cancer from benign nodules.

Cold nodules: Only 15% of cold nodules are malignant (cancerous). It is an old technology which is not specific. Nodules should be evaluated by ultrasound and needle biopsy. I rarely find it necessary to order this test. Khalid AN, Hollenbeak CS, Quraishi SA, Fan CY, Stack BC Jr. The cost-effectiveness of iodine 131 scintigraphy, ultrasonography, and fine-needle aspiration biopsy in the initial diagnosis of solitary thyroid nodules. Arch Otolaryngol Head Neck Surg. 2006 Mar;132(3):244-50. PubMed PMID: 16549743.